As part of the wellbore construction process, a hole or wellbore is typically drilled into the earth and then often lined with a casing or liner. Usually sections of casing or liner are threaded together or otherwise connected as they are run into the wellbore to form what is sometimes referred to as a “string.” Such casing may comprise a steel tubular “pipe” having an outer diameter that is smaller than the inner diameter of the wellbore. Because of the differences in those diameters, an annular area occurs between the inner diameter of the wellbore and the outer diameter of the casing. Absent the presence of anything else, wellbore fluids and earth formation fluids may migrate lengthwise along the wellbore in that annular area.
Wells are typically constructed in stages. Initially a hole is drilled in the earth to a depth at which earth cave-in or wellbore fluid control become potential issues. At that point, drilling is stopped and casing is placed in the wellbore. While the casing may structurally prevent cave-in, it will not prevent fluid migration along a length of the well in the annulus. For that reason, the casing is typically cemented in place. To accomplish that, a cement slurry is pumped down through the casing and out the bottom of the casing. Drilling fluid, water, or other suitable wellbore fluid is pumped behind the cement slurry in order to displace the cement slurry into the annulus. Typically, drillable wiper plugs are used to separate the cement from the wellbore fluid in advance of the cement volume and behind it. The cement is left to cure in the annulus thereby forming a barrier to fluid migration within the annulus. After the cement has cured, the cured cement remaining in the interior of the casing is drilled out and the cement seal or barrier between the casing and the formation is pressure tested. If the pressure test is successful, a drill bit is then run through the cemented casing and drilling is commenced from the bottom of that casing. A new length of hole is then drilled, cased, and cemented. Depending on the total length of well, several stages may be drilled and cased.
Unfortunately, the cements employed for the aforementioned operations often suffer from a variety of deficiencies. For example, the cements may not have sufficient strength, flexibility, or toughness to withstand the pressures, corrosion, and other stresses that may often be encountered downhole. Failure of the cement may lead to disastrous and expensive consequences to the well and/or the surrounding environment. Similarly, currently available cements may be cumbersome to process. For example, hexavalent chromium compounds and other particulates in the cement may require that special handling procedures are implemented so as to limit worker exposure to such hazardous materials. Accordingly, what is needed are new cement compositions and processes that solve one or more of these deficiencies with conventional cement used in downhole oil and gas operations.
Advantageously, the instant invention reduces or eliminates one or more of the mentioned deficiencies with the prior art cementing compositions and processes. In one embodiment the invention involves a novel method of cementing a well. The method comprises the step of pumping a suspension. The suspension comprises a filler mixture and at least about 5 weight percent of a thermosetting resin based on the total weight of resin and filler mixture. The suspension cures when subjected to a catalyst. The cured composition comprises one or more of the following characteristics (a) through (g): (a) a tensile strength of at least about 300, 1000, 1500 psi according to ASTM C1273 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity; (b) a compression strength of at least about 1500, 2000, 3000, 10,000 psi according to ASTM C873 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity; (c) a flex strength of at least about 500 psi, 750, 1000 according to ASTM C873 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity; (e) a fracture toughness of at least about 0.3 Mpa root meter, pref. 0.6, 08 according to ASTM C1421; (0 a ratio of tensile strength to compressive strength of at least about 10, 15%, 20, and 30 wherein the tensile strength is measured according to ASTM C1273 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity and the compression strength is measured according to ASTM 873 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity; and (g) a flex fatigue resistance such that the cured composition can be subjected to a stress of 50% of the cured composition's ultimate failure strength for at least 1000 cycles without breaking.
In another embodiment, the invention relates to a composition comprising: (1) from about 10 to about 25 weight percent of a thermosetting resin based on the total weight of the composition; (2) from about 15 to about 25 weight percent of a microscopic filler based on the total weight of the composition; (3) from about 30 to about 70 weight percent of an aggregate based on the total weight of the composition; and (4) an intercalatable nanoclay, an exfoliatable nanoclay, or a mixture thereof.
In yet another embodiment, the instant invention relates to a method of cementing a subterranean formation. The method comprises pumping a suspension comprising (1) from about 15 to about 25 weight percent based on the total weight of the suspension of a first component selected from the group consisting of calcium carbonate, talc, silica, and mixtures thereof; (2) from about 30 to about 70 weight percent based on the total weight of the suspension of a second component selected from the group consisting of crushed rock, gravel, sand and mixtures thereof; (3) from about 10 to about 25 weight percent based on the total weight of the suspension of a thermosetting resin; and (4) a catalyst capable causing the suspension to cure. The cured composition is characterized by a ratio of tensile strength to compressive strength of at least about 20 wherein the tensile strength is measured according to ASTM C1273 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity and the compression strength is measured according to ASTM 873 with a 0.01 inch/min of cross-head speed at ambient 25C at 50% humidity.